Cracking of hydrocarbons with steam or carbon dioxide



Oct- 19, 1965 R. G. ATKINSON r-:TAL 3,213,015

CRACKING OF HYDROCARBONS WITH STEAM OR CARBON DIOXIDE 2 Sheets-Sheet lFiled Feb. 25, 1965 55 w Sanoma @m2o/U N @www www Q M WA a 7 Oct 19,1965 R. G. ATKINSON ETAL 3,213,015

CRACKING OF HYDROCARBONS WITH STEAM OR CARBON DIOXIDE Filed Feb. 25,19ers 2 sheets-sheet 2 36^1` CRACKED PRODUCT, STEAM 28 AND COMBUSTIONGASES igmf INVENTORS RG. ATKINSON RL. ARNETT Mek A TTORNEKS` UnitedStates Patent O 3,213,015 CRACKING OF HYDROCARBONS WITH STEAM OR CARBONDIOXIDE Robert G. Atkinson, Idaho Falls, Idaho, and Raymond L.

Arnett, Bartlesville, Okla., assignors to Phillips Petroleum Company, acorporation of Delaware Filed Feb. 25, 1963, Ser. No. 260,532 9 Claims.(Cl. 208-130) This invention relates to the cracking of hydrocarbons. Inanother aspect, it relates to a process and apparatus for crackinghydrocarbons in the presence of steam, utilizing infrared radiation.

In the art of petroleum refining, it is a common practice to crackhydrocarbons by subjecting them to various thermal processes. Forexample, cracking stills or furnaces are used in which coils containingthe hydrocarbon are externally heated, or the hydrocarbon is sprayed ona bed of coke which is heated to incandescence. Other methods employchecker-brick regenerative furnaces or a moving or stationary bed ofsolid contact material such as pebbles or catalyst-impregnated bases.These thermal processes rely primarily upon the heating effects ofconduction and/or convection. While many of such processes do enjoycommercial exploitation, the many problems encountered, suchas coking,burn-out of tubes, the necessity for regenerating contact materials,etc., leave room for improvement. Also, such processes, particularlywhere black body radiation is generated, are not generally selective inthe cracking they cause to take place, the hydrocarbon molecules beingsplit in a random nature, often at the end of chains, usually with theproduction of large amounts of methane and other low molecular weightproducts.

Accordingly, an object of this invention is to improve the cracking ofhydrocarbons. Another object is to provide an improved process andapparatus for cracking hydrocarbons in the presence of steam, utilizinginfrared radiation. Another object is to provide an improved process andapparatus for converting hydrocarbons to certain cracked hydrocarbons inhigh yields without relying in the first instance on conduction andconvection, and in the absence of solid contact material, and with aminimum, if any, of black body radiation. Further objects and advantagesof this invention will become apparent to those skilled in the art fromthe following discussion, appended claims and accompanying drawing inwhich:

FIGURE 1 is an elevational view in cross section of one embodiment ofthe improved apparatus of this invention;

FIGURE 2 is a cross sectional View of FIGURE l taken along the planeindicated; and

FIGURES 3 and 5 are elevational views in cross section of otherembodiments of the improved apparatus of this invention, With FIGURES 4and 6 being cross sectional views thereof, respectively, taken along theplanes indicated.

In the improved cracking process of this invention7 the hydrocarbon feedto be cracked is admixed with a fluid which will absorb infraredradiation of select wavelength and the mixture is subjected to intenseinfrared radiation of said select wavelength emitted by the combustionproduct generated by a fuel gas-oxygen burner. The infrared absorberused preferably will be of the same chemical constituency as that of thecombustion product generated by the burner; for example, where the fuelgas is hydrogen, the combustion product generated will be Water, andthus the infrared absorber to be admixed with the hydrocarbon feed willbe Water, or if the fuel gas is a hydrocarbon, such as methane, in whichcase the combustion product will comprise both water and ice carbondioxide infrared emitters, the infrared absorber to be admixed with thehydrocarbon feed will be water aud/ or carbon dioxide.

Several different furnaces or reactor configurations can be used tobring about the intense infrared radiation of the hydrocarbon-infraredabsorber mixture, such furnaces being constructed so as to avoid theblack body radiation of the prior art and foster the selective crackingof the hydrocarbon feed. For example, the cracking of straight chainparains, such as those present in paratiin wax, is effected according tothis invention by splitting the hydrocarbon molecules near the center ofthe chains to form l-olefins (which can be converted to primaryalcohols, useful in the manufacture of biodegradable detergents)together with low molecular weight normal parains, with minimumformation of undesirable products, such as dienes, tar, methane, coke,etc.

The hydrocarbon-infrared absorber mixture is introduced into thefurnaces of this invention in such a manner that it immediately sees theinfrared radiation source provided by the fuel gas-oxygen burner; thatis, the hydrocarbon-infrared absorber mixture is: brought into thefurnace in such a manner that it does not first pass through combustiongases, heated product, or other foreign gases which would present abarrier between the infrared radiation source and thehydrocarbon-infrared absorber mixture.

The hydrocarbon in the hydrocarbon-infrared absorber mixture ispreferably in the gaseous or vaporous state, or in the form of a mist,and it is preferred to preheat the feed mixture before introducing thesame into the furnace. Such preheating can be accomplished in anyconventional preheater, by passing the hydrocarbon in indirect heatexchange with the products of conversion, or by circulating thehydrocarbon feed in a jacket surrounding the furnace, etc. The amount ofinfrared absorber employed can vary; generally the mole ratio ofinfrared absorber to hydrocarbon will be in the range of 0.001/1 to l/1,preferably in the range of 0.01/1 to 0.1/1.

The infrared absorber molecules in the hydrocarboninfrared absorbermixture introduced into the furnace readily absorb the infraredradiation emitted by the molecules of the infrared emitter formed incombustion of the fuel gas with oxygen. In the case of water, infraredradiation having wavelengths of about 2.7 and 6.2 microns will beemitted and absorbed; in the case of carbon dioxide, infrared radiationhaving wavelengths of about 4.3 and 15.0 microns will be emitted andabsorbed. Such infrared radiation is not absorbed to any significantextent by hydrocarbon molecules of the feed. The infrared absorbermolecules (e.g., water and/or carbon dioxide) are activated to highenergy levels, e.g., 1000u F., by absorbing said infrared radiation andtransfer this high energy immediately to the hydrocarbon molecules ofthe feed by conduction, causing the high molecular weight hydrocarbonmolecules to undergo a selective cracking reaction (with a minimum ofpyrolysis) which results in the splitting of hydrocarbon molecules atcarbon-carbon bonds near the center of the molecules to produce1-olefins (RCHzCl-I2) and :straight chain parans (RCH3) of about thesame molecular Weight. In order to foster this selective cracking, theprocess is carried out in the absence of a luminous llame (whichcontains soot or carbon particles, i.e., black body radiators), solidcontact material, firebrick, catalyst impregnated supports, or otherblack body radiators, and by using highly reflective material, such asstainless steel, chromium plated alloys, metallized quartz, etc., inconstruction of the furnaces of this invention.

Referring now to the drawing, in which like parts have been designatedwith like reference numbers, and initially to FIGURES 1 and 2, there isillustrated one embodiment the diameter of the top of the furnace willbe \/2 or about 1.4 times that of the bottom. This furnace, preferablymade from or lined with stainless steel, has an inlet tube 2 near thelower end for the introduction of the hydrocarbon-infrared absorber feedmixture and an outlet tube 3 near the upper end of the shell for thewithdrawal of cracked products and combustion products. Inlet 2 andoutlet 3 are preferably disposed tangentially with respect to theperiphery of shell 1, so that the feed mixture flows through the furnacein the form of an ascending helical stream adjacent the inner wall ofthe shell, as indicated by reference number 4. Axially disposed in thelower end of the furnace is a fuel gas-oxygen burner 6 which provides anon-luminous flame 7 that emits the infrared radiation of the selectivewave length mentioned above. Flame 7 is disposed axially within thehelically swirling hydrocarbon-infrared absorber mixture 4, and thecombustion gases from the burner can be removed via axial pipe 8 in thetop of the furnace, which pipe can depend some distance within thefurnace, as shown, with the lower end thereof flared out, so as tofurther minimize admixture of the combustion gases with the gaseouscracked product and thus simplify to some extent the separation andrecovery of desired components from the furnace effluent. Noteespecially that the hydrocarbon-infrared absorber feed mixtureintroduced via pipe 2 immediately sees the infrared radiationsource-there is no substantial foreign gaseous barrier obstructing thetransmission of this radiation to the 4introduced feedstock.

Fuel gas is supplied to burner 6 by line 9. Almost any type of fuel gascan be employed which will not give vrise to a luminous flame, though itis preferred that the fuel gas be relatively rich in hydrogen.

gas is hydrogen itself, but because of economical considerationshydrocarbon fuels such as natural gas, liquid petroleum gas, or thelike, will often be advantageous to use, these latter fuels generatingwater and carbon dioxide as combustion products which serve to emit theinfrared radiation and transfer energy to the corresponding infraredabsorber present in the feed, which energy is -thence transferred to thehydrocarbon molecules causing the same to crack. The oxygen employed bythe burner 6 .is supplied by line 11 and it should be relatively pure toprovide intense infrared radiation of the desired wave .length andminimize the presence of fixed gases, such as nitrogen. Air itself willnot be satisfactory because of the presence of nitrogen in the air,which nitrogen will cool the combustion flame and thus decrease theintensity of infrared radiation that is generated. The energy used toheat such nitrogen is lost to the cracking process. While combustion ofthe fuel gas with the oxygen will produce at least one species ofinfrared emitter as a combustion product, the fuel gas can be mixed withthe same material that is mixed with the hydrocarbon cracking feed as aninfrared absorber to augment the amount of infrared emitter generated bythe burner as a combustion product. For example, water (e.g., to 79percent) can be admixed with the hydrocarbon fuel gas-oxygen mixture,the amount of such water being sufficient to enhance the intensity ofthe infrared radiation generated.

The products of the cracking process, withdrawn from the furnace viatube 3, can be condensed in any suitable cooler and the desired crackedproducts, such as l-olens, can be separated from non-condensed gases andrecovered The ideal fuel by suitable conventional recovery equipment,such as distillation, etc.

Looking now at the embodiment shown in FIGURES 3 and 4, the furnacethere comprises a shell 13 which is an elliptical cylinder, and again ismade of a highly reilective material, such as stainless steel. Extendingalong part or all of one focus of the elliptical furnace 13 is a burnertube 14 having a plurality of spaced ports to provide sites for flames16, the infrared radiation emitters. Like FIGURE 1, burner 14 can beprovided with fuel gas 9 and oxygen 11. Disposed along the other focus0f the elliptical furnace 13 is a tube 17 to which hydrocarboninfraredabsorber feedstock is supplied via line 18. The feedstock tube 17 ismade of a material which is transparent, i.e., which transmits radiationpreferably through the wavelength the range of 2.7 to 15.0 microns, forexample, mica, quartz or such synthetic materials like Irtran. In thisembodiment of the furnace of this invention, all contact between thecombustion gases formed with the feedstock and cracked product areavoided, the combustion gases being withdrawn via outlet pipe 19(preferably with the aid of a blower 24 or the like) and the product ofthe process being withdrawn via line 22.

The elliptical nature of the embodiment of FIGURE 3 is such as toenhance the intensity of the infrared radiation received by thehydrocarbon-infrared absorber mixture, in that the infrared radiation isreceived by the mixture by direct wave paths, such as path 23, andreflected wave paths 24, 26. No foreign gaseous barrier is disposedbetween flames 16 and the feed in tube 17.

In the embodiment of the furnace shown in FIGURES 5 and 6, thecylindrical shell 28, again made of a highly reflective material such asstainless steel, is provided with anvaxial burner 29, like that ofFIGURE 1, again with suitable fuel gas being supplied via line 31 andOxygen supplied via line 32. Surrounding burner 29 is a tubular ring 33for introduction into the furnace of the hydrocarbon-infrared absorbermixture, the ring 33 being provided with a plurality of apertures 34 topermit injection of the mixture as a gaseous cylinder. As in the case ofthe embodiment for FIGURE l, the introduced hydrocarbon-infraredabsorber mixture immediately sees the infrared source 34. The productsof combustion and products of hydrocarbon conversion can be removed fromthe shell 28 by means of a common axial outlet pipe 36 in the upper endof the furnace. Alternatively, pipe 36 can depend within shell 28 in themanner shown in FIG- URE 1, and another outlet pipe provided in the topof the shell 28 for withdrawal of the products of cracking, so as tominimize mixture of the two and simplify the separation and recovery ofdesired cracked components.

FIGURE 5 also illustrates a scheme for mixing the hydrocarbon with theinfrared absorber, e.g., water, namely by aspiration of hydrocarbon 37from a tank 38 into a line 39 by means of an aspiratorvpipe 41. (Thistechnique can be employed in any of the embodiments of this invention.)The resulting mixture of the infrared absorber and hydrocarbon is thenpassed via one or more supply lines 42 to the injection ring 33.

As an example of this invention, referring to FIGURES 1 and 2,n-hexadecane at the rate of one gallon per minute (6.9 lbs/min.) ispreheated and vaporized to yield 11.6 s.c.f. per min. of hexadecanevapor at 700 F. This vaporous hydrocarbon is mixed with steam and passedat 5 p.s.i.g. via line 2 into the shell 1 of the furnace, which is 3 ft.in height with bottom diameter of 1 ft. and a top diameter of 2 ft. Acombustible mixture comprising 7% methane, 14% oxygen and 79% steam, isburned by burner 6 to produce a flame 7 having a temperature of 1100 F.Such combustion produces infrared radiation of 2.7, 4.3, 6.2 and 15.0microns. This radiation is absorbed by the steam in thehydrocarbon-steam feed and the energy from these irradiated molecules istransferred to the hydrocarbon withdrawn from the shell 1 of the furnace`via outlet pipe 3 and passed to a cooler. The

cooled etlluent is then passed to a gas-liquid separator, from which isrecovered 3900 cc. of liquid product (comprising 1900 cc. of C6 to C10l-oleins), and uncondensed gases (2% of feed).

As a comparison, the same hydrocarbon-steam mixture described in theexample above is passed to a single tube heater measuring 4 in. innerdiameter and 10 ft. in length, where the mixture is heated to ll00 F.The gaseous eluent therefrom is similarly cooled and condensed, yieldinga gaseous product amounting to 25 weight percent of the feed (comprising17% hydrogen, 20% methane, 21% C2 and saturates and 42% oleiins) and2900 cc. of liquid product (comprising 1800 cc. of uncracked hexadecane,500 cc. of C4 to C12 paraflins, 500 cc. of C4 to C12 olens, and 100 cc.of diolefins and tar).

Various modifications and alterations of this invention will becomeapparent to those skilled in the art from the foregoing discussion andaccompanying drawing without departing from the scope and spirit of thisinvention, and it should be understood that this invention is not to belimited unduly to that set forth herein for illustrative purposes.

We claim:

1. A process for cracking hydrocarbons which comprises mixing saidhydrocarbons with a compound selected from the group consisting ofsteam, carbon dioxide and mixtures thereof;

passing a combustible fuel and oxygen in admixture which formscombustion products comprising the chemical composition of said selectedcompound into a conversion zone;

combusting said fuel in said conversion zone to produce an infraredradiation source;

passing said hydrocarbons in admixture with said selected compounds intosaid conversion zone in unobstructed communication with said infraredradiation source whereby the infrared radiation emitted by said sourceis absorbed unaltered in wavelengths by said selected compounds;

withdrawing the resulting gaseous eliiuent from said zone; and

separating the desired cracked hydrocarbon products from said efliuent.

2. The process of claim 1 wherein said hydrocarbonsselected compoundadmixture is introduced into said conversion zone tangentially to saidfuel-oxygen admixture.

3. The process of claim 2 wherein said selected compound is steam andsaid fuel is hydrogen.

4. The process of claim 2 wherein said selected compound is a mixture ofsteam and carbon dioxide and said fuel is a hydrocarbon gas.

5. The process of claim 1 wherein said fuel-oxygen admixture isintroduced axially into the lower portion of said conversion zone andsaid hydrocarbons-selected compound admixture is introduced laxiallyinto the lower portion of said conversion zone and circumscribing saidfuel-oxygen admixture.

6. Apparatus for cracking hydrocarbons, which comprises a frusto conicalreaction chamber formed of highly reflective materials, a fuelgas-oxygen burner axially disposed in the bottom of said chamber, thediameter of said chamber increasing from bottom to top, means tot-angentially introduce a hydrocarbon-steam mixture into the lower endof said chamber whereby unobstructed communication is provided betweensaid burner and said mixture, means to axially remove combustion gasesfrom the top of said chamber, and means to tangentially remove gaseouscracked product from the upper end of said chamber.

`7. A lhydrocarbon cracking furnace which comprises an invertedtruncated cone housing, a burner axially positioned at the base of saidhousing, a first conduit communicating with said burner for passing fueland oxygen thereto which produces infrared rays, a second conduittangentially communicating with the lower portion of said housing forintroducing hydrocarbon feed material, whereby unobstructedcommunication is provided between said burner and said hydrocarbon feed,a cylindrical hood depending axially from the top of said housing andcommunicating with a third conduit extending therefrom for removingcombustion gases from said housing, 'and a fourth conduit tangentiallycommunicating with the upper portion of said housing for removingcracked feed therefrom.

8. Apparatus for cracking hydrocarbon which comprises a horizontalelliptical shaped housing, a burner longitudinally disposed along onefocus of the housing, a plurality of openings in said burner, a rstconduit communicating with said burner for introducing fuel and oxygenwhich produces infrared rays, an infrared transparent chamber disposedlongitudinally along the other focus of said housing, a second conduitcommunicating with said chamber for introducing hydrocarbon feedmaterial, a third conduit communicating with the opposite end of saidchamber for removing cracked product therefrom, and a fourth conduitcommunicating with said housingr for removing combustion gasestherefrom, the communication between said burner and sai-d hydrocarbonfeed being otherwise unobstructed.

9. Apparatus for cracking hydrocarbons which comprises a housing, aburner axially positioned in the base of said housing, means forintroducing fuel and oxygen to said burner which produces infrared rays,manifold ring having a plurality of openings therein disposed about saidburner within said housing, means for 4introducing hydrocarbon feedmaterial to said manifold whereby unobstructed communication is providedbetween said burner and said hydrocarbon feed, and means axiallypositioned at the top of said housing for removing cracked product andcombustion gases.

References Cited by the Examiner UNITED STATES PATENTS 2,172,228 9/39Van Peski 208-106 2,397,899 4/46 V-Jitkiewiez 23-2889 3,0l8,309 1/62Krejci 260--679 ALBHONSO D. S'ULLVAN, Primary Examiner.

1. A PROCESS FOR CRACKING HYDROCARBONS WHICH COMPRISES MIXING SAIDHYDROCARBONS WITH A COMPOUND SELECTED FROM THE GROUP CONSISTING OFSTEAM, CARBON DIOXIDE AND MIXTURES THEREOF; PASSING A COMBUSTIBLE FUELAND OXYGEN IN ADMIXTURE WHICH FORMS COMBUSTION PRODUCTS COMPRISING THECHEMICAL COMPOSITION OF SAID SELECTED COMPOUND INTO A CONVERSION ZONE;COMBUSTING SAID RUEL IN SAID CONVERSION ZONE TO PRODUCE AN INFRAREDRADIATION SOURCE; PASSING SAID HYDROCARBONS IN ADMIXTURE WITH SAIDSELECTED COMPOUNDS INTO SAID CONVERSION ZONE IN UNOBSTRUCTEDCOMMUNICATION WITH SAID INFRARED RADIATION SOURCE WHEREBY THE INFRAREDRADIATION EMITTED BY SAID SOURCE IS ABSORBED UNALTERED IN WAVELENGTHS BYSAID SELECTED COMPOUNDS; WITHDRAWING THE RESULTING GASEOUS EFFLUENT FROMSAID ZONE; AND SEPARATING THE DESIRED CRACKED HYDROCARBON PRODUCTS FROMSAID EFFLUENT.